An earth leakage detector, such as an earth leakage breaker and an earth leakage relay for electric shock prevention, which has been developed for the purpose of preventing electrification fatal and injury accident with mobile-portable electric machinery and appliance in accordance with occupational safety and health regulations, has become popular for its low cost and ease of use. For this reason, this earth leakage detector has been also in heavy usage for electrical shock prevention, leakage alarm and earth blocking in even stationary industrial production installations.
In recent years, the number of equipments containing highly-developed control systems has been getting increased in an electrical load installation. For the purpose of preventing a wide-area scattering of noise power components generated from the equipments or an erroneous operation of the installation, a noise canceller having a high-volume capacitance stands besides the installation. Due to this parallel establishment of the noise canceller, the productivity is fraught with obstacles, for example, increased regular leakage current, blackout or unnecessary alarm caused by an unnecessary suffered operation due to a suffered current derived from a ground fault on the side of a power source of the installation, etc.